Hitherto, there has been known a micropump using a piezoelectric element which undergoes bending deformation in a bending mode by application of a voltage. Patent Document 1 discloses a micropump in which a pump chamber is formed in a pump body, and a piezoelectric element is attached onto a back surface of a diaphragm which defines a top wall of the pump chamber.
FIG. 9(a) schematically illustrates a pump structure described in Patent Document 1. A pump chamber 21 is provided in a case 20. A piezoelectric element 23 is attached onto a diaphragm 22 which defines a top wall of the pump chamber 21. The diaphragm 22 is formed of an organic material such as polyimide. However, referring to FIG. 9(b), when the piezoelectric element 23 undergoes bending deformation, a change in volume of the pump chamber 21, which is expected to be generated by bending of the piezoelectric element 23, partly becomes inefficient as a result of a displacement of the diaphragm 22 at both end portions of the piezoelectric element 23. In other words, the piezoelectric element 23 is merely moved in a floated manner via the diaphragm 22. Hence, a displacement of the piezoelectric element 23 cannot be transmitted as a change in volume of the pump chamber 21. This phenomenon occurs because, for example, when the piezoelectric element 23 is deformed to bulge toward the pump chamber 21 so as to pump out incompressible fluid (liquid) filled in the pump chamber 21, a pressure of the liquid is applied to the diaphragm 22, and a peripheral portion of the diaphragm 22 (portion where the piezoelectric element 23 is not attached) is displaced in a reverse direction away from the pump chamber 21 by the pressure of the liquid. In contrast, when the piezoelectric element 23 is deformed to bulge away from the pump chamber 21, the peripheral portion of the diaphragm 22 is bent toward the pump chamber 21.
When the diaphragm 22 is formed of a hard material such as a metal plate, bending of the peripheral portion of the diaphragm 22 can be inhibited, and hence, the phenomenon as shown in FIG. 9(b) does not occur. However, if the diaphragm 22 is hard, the diaphragm 22 inhibits the bending deformation of the piezoelectric element 23, thereby decreasing the amplitude of the bending deformation and the change in volume of the pump chamber 21. Also, a drive frequency of the pump is decreased, and hence, fluid transportation performance is deteriorated. Further, in the known configuration, unless the piezoelectric element 23 is attached to the center of the diaphragm 22, the left-right balance of a displacement is disrupted, and the change in volume of the pump chamber 21 cannot be correctly transmitted. Thus, it is necessary to increase a positional accuracy of attachment between the diaphragm 22 and the piezoelectric element 23.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2003-214349